Universal rotation method and apparatus for locating axes in single spherical ferrimagnetic crystals



, M. F. AUER 3,183,434 UNIVERSAL ROTATION METHOD AND APPARATUS FOR LOCATING AXES IN SINGLE SPHERICAL FERRIMAGNETIC CRYSTALS Filed Oct. 50, 1961 May 11, 1965 FIG. 2 I8 2 R.. W 5; m 2 WWW 4 \AAMwW m M r r 8 9 lull w? M IHLIIIINMWMIILTIILH v @M/JW M] \w m \m H Mr 7 I 2 Q a m. Q p ill Ill l I 0 "m If '00 4 v {I 2 8 w 11 um 2 mm Q 4% E3 57 0, ||ll| ATTORNEY.

United States Patent UNIVERSAL ROTATION METHGD AND APPA- The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

This invention relates to a method and means for orientin g ferrimagnetic crystals along their crystallographic axes and particularly to orienting such crystal of spherical conformation.

Prior to the present invention the crystallographic axes of ferrimagnetic crystals were located by the well known- X-ray technique. This procedure necessitates the use of expensive apparatus, requires skilled specially trained operators and is a time consuming operation.

The present invention embraces a simplified and speeded up technique for accomplishing orientation of the crystals, without the complication, expense and time consuming practice involved in the X-ray technique. The present invention is effective in the orientation of crystals of various physical shape but is particularly directed to crystals of spherical form. Such spherical crystals present diflicult problems of manipulation and marking when locating the critical axes thereof by existing methods. Such ditficulties are solved by the present invention.

' In the application of single crystal ferrimagnetic crystals to electronic devices accurate knowledge of their anisotropic properties is essential. Such properties as saturation magnetization, resonance line width and magnetostriction are dependent on the orientation of the crystal axes with respect to the external field which is associated with the crystal in many electronic devices. Alignment of the applied field with any one of the crystal axes will produce either a maximum, minimum or intermediate value of the investigated property of the crystal.

For many applications and research studies the spherical crystal has been a favored conformation. It will become evident hereinafter that the present invention is ideally adapted to rapidly and efficiently orient such crystals.

It has been found that one of the easy crystallographic axes of ferrimagnetic materials will align itself with the flux lines of an applied magnetic field if the crystal is free to rotate in any direction. This property is utilized in the present invention to produce the desired result. Means are provided to support the crystal and simultaneously to provide free universal rotation thereof. Such means consists of floating the crystal on a pool of liquid having low viscosity and a specific density greater than that of the crystal. Mercury has been found to be a satisfactory material for this purpose.

The sample sphere is placed upon a pool of mercury and a strong magnetic field is applied thereto. The field strength may be of the order of 3000 gauss although the field strength may vary within Wide limits. By so doing the sample will rotate until an easy axis of the crystal will align itself with the flux lines of the field. Thus the orientation of the crystal will indicate the position of this easy axis.

A second easy axis may then be found by first removing the field and manipulating the crystal into a position estimated to be approximately that which will disposed the second axis in line with the field lines. The field is then 7 3,183,434 Patented May 11, 1965 reapplied and the crystal will accurately align itself upon the second easy axis. 4

As will appear from the following more detailed explanation the positions of the two easy axes provide the basis for geometrically locating other desired axes of the crystal such as the hard axis or the intermediate axis.

It is a primary object of the invention to provide improved means for locating crystallographic axes in ferrirnagnetic spheres.

A further object of the invention is to provide a tech nique for locating crystallographic axes in ferrimagnetic spheres without the use of X-ray apparatus.

A still further object of the invention is to provide a magnetic orienting system for spherical ferrimagnetic crystals wherein the crystal is floated upon the surface of a liquid.

A further object of the invention is to provide a technique for locating and marking the position of the useful crystallographic axes in ferrirnagnetic spheres and particularly in spheres having diameters as small as 1 millimeter.

Other objects and features of the invention will more fully appear from the following description and will be particularly pointed out in the claims.

To provide a better understanding of the invention particular embodiments thereof will be described and il-' .lustrated in the accompanying drawings wherein:

FIGS. 2 and 3 are diagrammatic views showing the relative positions of various crystallographic axes within cubic single crystals.

FIG. 4 is a general elevation of an apparatus for aiding in marking the position of the axes which have been located within the crystal.

The basic elements for the practice of the invention are shown somewhat diagrammatically in FIG. 1. The spherical crystal 10 has been accurately formed to spherical shape and preferably its surface is given a smooth finish. The crystals illustrated and described herein are small ranging from approximately 1 to 2 millimeters in diameter, but larger crystals may be investigated in the same manner as that described herein. The crystal 10 may be made of any suitable ferrimagnetic material such as YIG, NiFe O MnFe O or Fe O The crystal is floated upon a pool of mercury 11 held in a container 12. The crystal and mercury pool are received between the poles of a powerful magnet 13 which may be a permanent magnet but preferably is an electromagnet having means to control the current in the windings and to turn it on and off. Also shown is a marking needle 14 for indicating the position of the located axis.

To orient the crystal it is placed on the surface of the mercury and the magnet is energized. The crystal being free to rotate in all directions will move until one of its easy axes 15 aligns itself with the direction of the magnetic flux lines and remains in this position. A small dot of marking fiuid is then placed upon the surface of the crystal at the point where the desired axis thereof passes through the center of the sphere parallel to the flux.

The magnetic field is then removed and the crystal moved into a position estimated to be approximately that in which a second easy axis is in alignment with the magnetic flux lines. The field is then restored which causes the crystal to move into accurate position locating a second easy axis 16. Trial and error may be necessary to avoid the tendency of the crystal to again align itself into its first located axial position. The second axis thus located is then marked by hand or With a guidance of a device to be described hereinafter.

By thus locating two easy axes within the crystal an accurate geometrical basis is established for determining the other useful axes of the crystal. FIG. 2 of the drawings shows the angular relationships of the magnetization axes in a cubic crystal of yttrium iron garnet type. It will be noted that in this material where the body diagonals lie in the easy direction an intermediate axis -17 is found in a direction represented by the bisecting line of two easy axes 15 and 16 when they are 7Q apart. In this same siturati'on a hard axis will be found in a direction which is given by the bisecting line of two easy axes when they are 110 apart.

FIG. 3 illustrates the angular relationships of the magnetization axes in a cubic crystal of the cobalt ferrite or cobalt iron oxide type. In this material the cube edge represents the easy axis 19 and the intermediate axis is found in a direction represented by the bisecting line 21 of two easy axes such as the axes 19 and 26. A hard axis 22, now the body diagonal, will be found in a direction which is 35% apart from the bisecting line 21.

In the case of the hexagonal crystal structure when the easy direction lies along the c-axis, which is parallel to the line of junction between hexagonal surfaces, the hard direction is anywhere within a plane perpendicular to the c-axis. When the caxis is the hard direction it may be found at an angle of 90 from the easy plane which is found from the markings of two easy directions.

It is believed to be evident from FIG. 2 of the drawing that upon the location of two easy axes in the crystal a definite plane is established and that a line parallel to this plane bisecting the 70 angle between the two easy axes establishes the intermediate axis of the crystal and that the hard axes is found in the same plane at the bisecting line When the angle between the easy axis is 110.

In the CFe O type material the various axes are found in a similar manner to that shown in FIG. 3 except for i the difference in the angles involved.

The marking of the various axes in the crystals as above stated may be done by hand however Where a higher order of accuracy is required it may be desirable to employ a mechanical system for accurately positioning the marking needle with respect to the crystal while the crystal is held in the magnetic field.

A suitable mechanism for this purpose is shown in FIG. 4 of the drawings wherein the various elements thereof are mounted in a nonmagnetic metallic base 23 within which the nonmagnetic container 12 for holding the mercury 11 is secured. All the parts of (the mechanism within the magnet field are made of nonmagnetic materials. The base 23 is received between the poles of the magnet 13 and is supported therein in any suitable manner as by resting upon a wooden block 24.

A hollow rigid tube 25 is fixed in the base and extends vertically to a point above the magnet poles. Received within the tube is a plunger 26 having a close but free running fit within said tube. The upper end of the plunger is screw threaded and has received thereon an adjusting wheel 27 the periphery of which is divided into suitable increments such as thousandths of an inch. The under surface of the wheel rides upon the end of the tube 25. The wheel 27 is held in contact with the tube by a tension spring 28 anchored in the bottom of the tube. The upper end of the plunger has rigidly secured thereto a horizontal supporting bar 29 for carrying the marking needle bar 30. A guiding post 31 is rigidly secured in the base 23 and extends vertically upward and through a slot 32 in the free end of the bar 29. The slot embraces the end of the post 31 and serves to maintain fixed alignment of the bar 29 while it is adjusted up or down bythe wheel 27.

The needle bar 30 is flexible and has its upper end secured to the bar 29 while its lower end is shaped into a horizontally disposed sharp point projecting toward the crystal. Sufficient spring tension is developed in the needle bar to hold it in contact with an adjustingscrew 33 which has threaded engagement with a rigid post 34 fixed to the bar 29. The screw 33 is provided with an operating wheel 35. Thus the needle point may be delicately moved into contact with the crystal by manipulating the wheel 35 while the vertical position of the needle point is under the control of the wheel 27. A pointer '36 desirably is fixed to the bar 29 and positioned to act as a reference point for the graduation of the wheel 27.

To operate the marking mechanism the needle point is adjusted in height until it is tangent to the top of the crystal and then is adjusted downward for one half the known diameter of the crystal which placesthe point in the horizontal plane of the desired axis. To locate the vertical plane containing the wanted axis opposite the needle point a gauge or some accurate measuring device such as an inside micrometer gauge is used to measure from the crystal to the side of the container 12. a distance which has been predetermined to place the crystal within the vertical plane of desired axis in line withathe needle.

Marking fluid is then placed on the point of the needle and the needle is moved into contact with the crystal to thereby mark the position of the axis. The second axis is then located in the manner indicated above and its location is marked.

From the marking the these two easy axes the remaining axes may be found following the general procedure outlined above. To aid in accomplishing this it may be convenient to mount the crystal bearing. the easy axes markings upon a block having a depression therein to receive the crystal and viewing the crystal with an optical magnifying means with or without a reticule therein. By manipulation of the crystal in the block other axes may be found such as the intermediate axis bet-ween the.

two easy axes.

For convenience in handling while checking and investigating the properties of the crystal under various conditions it is desirable to mount the crystal upon a holding means such as a small rod of Teflon or other suitable material. An example of a technique for so mounting the crystal is as follows. When the intermediate axis is found and oriented in a vertical direction the rod having a small quantity of adhesive thereon is touched to the crystal and held vertically until the adhesive hardens. By rotating the rod the crystal will then display all three of the main axes in a plane normal to its axis of rotation.

What is claimed is:

1. A method of locating crystallographic axes in single crystal spherical ferrimagnetic crystals comprising floating the spherical crystal upon the surface of a stationary pool of mercury, applying a magnetic field to the crystal.

with the flux lines extending substantially parallel to the mercury surface whereby an easy axis of the crystal will align itself with the flux lines, positioning the point of a marking stylus upon the horizontal plane which bisects said crystal, positioning said crystal so that the vertical plane in which said marking stylus lies substantially bisects said crystal, said vertical plane being parallel to the flux lines, applying marking material to said point and moving said stylus along the line formed by the intersection of said horizontal and said vertical planes until it contacts said sphere thereby marking a spot on the sphere which locates an easy axis of the crystal.

2. Apparatus for locating crystallographic axes in single crystal ferrimagnetic spherical crystals comprising a magnet having spaced pole pieces, a small open pool of mercury supported horizontally in the magnetic field between said pole pieces, the mercury pool being positioned to place a ferr-imagnetic sphere at the most uniform por tion of the magnetic flux, the sphere being freelyfloated upon the mercury surface where it submerges less than one halfof its volume in the mercury whereby the magnetic flux will cause the crystal to rotate universally until an easy axis therein will align itself parallel to the said flux lines, aneedle bar having a marking needle point 5 6 thereon juxtaposed to said crystal, transferable marking References Qited by the Examiner material on sai d needle point, micrometer means for UNITED STATES PATENTS vertically ad usting the height of said needle point to he 7 upon the horizontal axial plane which bisects said crystal 9 Emm- 7 324*14 X whereby manipulation of the crystal may be accomplished 5 9/39 Franklin to place its easy axis in alignment with said needle point 2182859 12/39 Wnght 324- 14 X while the magnetic field maintains the easy axis of said L643 17 4/53 Marchand et 8 324544 crystal parallel to the field lines and micrometer means FOREIGN PATENTS to move said needle point along said easy axis to engage the crystal thereby depositing marking material upon the 254307 9/27 Great Bntam sphere upon an easy axis thereof. WALTER L. CARLSON, Primary Examiner. 

1. A METHOD OF LOCATING CRYSTALLOGRAPHIC AXES IN SINGLE CRYSTAL SPHERICAL FERRIMAGNETIC CRYSTALS COMPRISING FLOATING THE SPHERICAL CRYSTAL UPON THE SURFACE OF A STATIONARY POOL OF MERCURY, APPLYING A MAGNETIC FIELD TO THE CRYSTAL WITH THE FLUX LINES EXTENDING SUBSTANTIALLY PARALLEL TO THE MERCURY SURFACE WHEREBY AN EASY AXIS OF THE CRYSTAL WILL ALIGN ITSELF WITH THE FLUX LINES, POSITIONING THE POINT OF A MARKING STYLUS UPON THE HORIZONTAL PLANE WHICH BISECTS SAID CRYSTAL, POSITIONING SAID CRYSTAL SO THAT THE VERTICAL PLANE IN WHICH SAID MARKING STYLUS LIES SUBSTANTIALLY BISECTS SAID CRYSTAL, SAID VERTICAL PLANE BEING PARALLEL TO THE FLUX LINES, APPLYING MARKING MATERIAL TO SAID POINT AND MOVING SAID STYLUS ALONG THE LINE FORMED BY THE INTERSECTION OF SAID HORIZONTAL AND SAID VERTICAL PLANES UNTIL IT CONTACTS SAID SPHERE THEREBY MARKING A SPOT ON THE SPHERE WHICH LOCATES AN EASY AXIS OF THE CRYSTAL. 